Vehicles, such as a recreational vehicle or semi-trailers, incorporate extendible legs to support, level, or raise the vehicle. Semi-truck trailers utilize extendible legs as landing gear legs in a landing gear assembly to raise and support the front of the trailer when disengaged from a semi-truck tractor.
Recreational vehicles, such as motor homes, trailers, and the like, often include one or more extendible legs proximal each end of the recreational vehicle. The legs can be extended individually, or as part of a vehicle leveling system, such as disclosed in U.S. Pat. No. 5,176,391, to level the recreational vehicle.
A typical semi-truck tractor and trailer are attached utilizing a “fifth wheel” type connection. A fifth wheel connection has a lubricated flat swivel plate and catch assembly mounted on the semi-truck tractor to engage a corresponding lubricated flat swivel plate and downwardly protruding “king pin” mounted on the underside of the forward portion of the trailer. The trailer king pin is received in a slot in the tractor swivel plate where it engages the tractor catch assembly locking the tractor and trailer together.
In order to disengage the tractor from the trailer, landing gear legs mounted on a forward section of the trailer are extended to the ground raising the king pin upwardly disengaging it from the catch assembly. Upon disengagement, the tractor pulls away from the trailer which is now supported by trailer rear wheels and the landing gear.
Known extendible legs, suitable for use as a landing gear leg and leveling leg, such as disclosed in U.S. Pat. No. 4,307,896, are formed with interfitting box-section supporting members. In U.S. Pat. No. 4,307,896, the interfitting box-sections have a axially driven ground engaging member telescopically interfitted with a box-like fixed member which is mounted to the vehicle. The ground engaging member telescopes between a retracted position and an extended position.
Typically the axially driven ground engaging member is manually or electrically driven in the telescoping direction. The driven member can be damaged when the driven member abruptly reaches the end limit of travel at either the extended or retracted position. In electrically driven landing gear, when the driven member abruptly reaches the end limit, the motor forming part of the drive mechanism remains energized until the operator turns the motor off, or the motor amperage exceeds a predetermined level which signals a control system controlling the motor to deenergize the motor. The sudden stop at the end limit can damage the drive mechanism and/or the members, and continued energization of the motor can cause the motor to overheat.
In recreational vehicle leveling legs, in order to withstand the forces exerted on the legs, the leg members are typically formed from tubes formed to tight tolerances to minimize gaps between the fixed leg member and the driven leg member. Providing tubes built to tight tolerances increases the cost of the leg. The tubes then form part of welded assemblies that provide a rigid structure to further strengthen the leg. Unfortunately, the welded assemblies are practically impossible to disassemble. As a result, if an internal component, such as a bearing, nut, thread screw, and the like fail, the entire landing gear is replaced.
Legs having a ground engaging member axially driven by a thread screw engaging a nut have additional problems. Radial and axial forces exerted on the thread screw are transferred to a drive shaft extending from the landing gear drive mechanism and rotatably driving the thread screw. These forces can cause the drive mechanism to bind and/or prematurely fail. In addition, side loads exerted on the ground engaging member of the landing gear can misalign the screw with the nut causing the screw and nut to bind or completely fail. Accordingly, a need exists for an improved extendible leg that overcomes one or more of the above problems.